First attempt with Graphviz:

Actually I started with the template listing what was not requested by this issue:

The upcoming uploaded patch(es):

• resolve direct parents and childes up to configured value for 'Max count of elements to show inside table cell' (for template list)
• resolve all parents and childes recursively (for edited template)
• render a PNG on-the-fly and embed it at its place.

I think of using SVG later at least in the template list to add proper hyper-links of the respective objects. That would then make the columns 'Linked templates' and 'Linked to' obsolete and save some space.

Further I think of combing the template list patch with ZBXNEXT-1796 to save even more space and get a nice listing.

I'm expecting to upload the patches tomorrow, err. today after having a sleep

If I had known it would become that easy, I had done this much sooner.

The attached patch zbxnext2100-2.2.5.patch implements mentioned functionality.

Finally it's one patch instead of two.

Additionally to the already mentioned changes the patch adds a linkage overview to hosts as well:

Edit:
The patch is not meant to represent a final solution. It's rather meant as a prove of concept.

Beside applying the patch graphviz's php library is needed (graphviz-php on EL6).

Attached patch zbxnext2100-2.2.5-2.patch includes some minor improvements and adds hyper-links to hosts and templates in list view of templates:

Because hyper-links are enabled by an image map the colors are hard coded and not set by CSS.

Since treating this as a POC and due to the fact that upstream devs would probably rather create their own Graphviz-like classes when considering this for implementation, I don't plan to add setting of colors based on themes CSS.

Btw, unfortunately I was not able to get hyper-links be written underlined. This appears to be limited by the EL6 distributed Graphviz version that does not support this yet.

Attached patch zbxnext2100-2.2.5-3.patch adds visualization to Configuration->Hosts as well:

Surely by now something similar to ZBXNEXT-1796 might be beneficial.

Attached patch zbxnext2100-2.2.5-4.patch fixes an 'Undefined index' issue on creation of new hosts.

Attached patch zbxnext2100-2.2.5-5.patch moves the inheritance diagram from the separate tab to the 'Linked templates' tab.
Additionally one can choose between four different resolution methods for templates:

Attached patch zbxnext2100-2.2.5-6.patch moves label to same level of radio buttons

Attached patch zbxnext2100-2.2.5-7.patch corrects radio button text and fixes root node not being bold when 'Follow both' (prev. 'Follow parents and childs') is selected.